The present invention relates generally to automatic transmissions for automotive vehicles, and more particularly to a power transmission mechanism for an automatic transmission, configured to establish seven or more forward speeds and one or more reverse speed.
A Published Japanese Patent Application Publication No. 2000-266138 (hereinafter referred to as “JP2000-266138”) shows a power transmission mechanism for an automatic transmission, configured to establish seven forward speeds and one reverse speed. This power transmission mechanism includes a compound planetary gearset as an input section, a pair of planetary gears as an output section, three clutches, a one-way clutch, and four brakes. The compound planetary gearset on the input side includes a sun gear, a ring gear, a secondary ring gear, and a planet-pinion carrier supporting a short planet pinion in mesh with the secondary ring gear and a long planet pinion in mesh with the short pinion and the sun gear on the input side and with the ring gear on the other side. The power transmission mechanism is configured so that gear shift from one speed to another next speed is performed by changing only one of the engagement states of the torque transmitting mechanisms including the clutches and the brakes.